Syntheses of high-spin and cluster molecules

Hiroki OSHIO (University of Tsukuba)

Syntheses and Magnetic measurements Dr. M. Nihei, A. Yoshida, K. Koizumi, Yamashita (Univ. of

Tsukuba )

Dr. M. Nakano (Osaka Univ.)

HF-EPR Prof. H. Nojiri (Okayama Univ.)

Low-temperature Magnetic measurements Profs. A. Yamaguchi and Ishimoto (ISSP, Univ. of Tokyo)

Solid State NMR Profs Y. Fujii (Fukui Univ.) and T. Goto (Kyoto Univ.)

Workshop on Nano-magnets at Kyoto, Dec. 1 - 4, 2003

Syntheses of

· SMMs of Ferrous Cubes: Structurally controlled magnetic anisotropy

· Mixed Valence Fe clusters· Hetero-metal SMM

Single Molecule Magnets[Mn(III,IV)12O12(O2CR)16(H2O)] (S = 10) (T. Lis, 1980)[Mn(III,IV)12O12(O2CR)16(H2O)4]- (S = 19/2)[Mn(III,IV)4O3X(O2CMe)(dbm)3] (S = 9/2)[Fe(III)8O2(OH)12(tacn)6]8+ (S = 10)[V(III)4O2(O2CR)7(L-L)]+ (S = 3)

D. N. Hendrickson, G. Christou, and D. Gatteschi (1993)

S = 10, D = –0.46 cm-1 L. Thomas et al., Nature 1996, 383, 145

[Mn12O12(OAc)16(H2O)4] [FeII4(sae)4(MeOH)4]

H. Oshio et al., J. Am. Chem. Soc. 2000, 112, 12602

S = 8, D = -0.28 cm-1

Syntheses of SMM

E

Magnetization Direction

E = |D|Sz2

E :Energy barrier to reorientate between two possible directions of magnetizationsD : Zero Field Splitting parameters

Relatively high-spin ground stateNegative D value

Strategy for the High-spin Molecule

Ferromagnetic Interactions by LMCT interactionsAGK TheoryP. W. Anderson (1959), J. B. Goodenough (1958), J. Kanamori (1959)

M

X

M'

Orthogonal Magnetic Orbitals

Strict orthogonality

MX

M

Orthogonal Arrangement ofMagnetic Orbitals

Accidental orthogonality

High-spin Cluster

O

O

MO

M

M

M

O Orthogonal arrangements of the magnetic orbitals

OH N

HO

OH N

HO

OH N

HO

OH

CH3

H2R-sae H2R-sap H2sapd

RR

Fe(II) Cube of [FeII4(sae)4(MeOH)4]

triclinic P1-a = 13.3625(7) Å, b = 13.7572(7) Å, c = 14.2004(7) Å= 66.538(1)°, = 74.973(1)°, = 71.105(1), V = 2239.92(1) Å3, Z = 2 R1 = 0.0477, wR2 = 0.0959

J. Am. Chem. Soc. 2000. 122. 12603.

S = 8 (4x2)

O- N

O-[sae]2-

AC measurements of [FeII4(sae)4(MeOH)4]

Relaxation in [Fe4(sae)4(MeOH)4] with S =8 Ground State

* R. Sessoli, D. Gatteschi et al.Nature 1996, 383,145.

3.01.1

-0.42-0.31

6128

[Mn12O12]

S =10*

[Fe4O4]

S = 8

Block. Temp.

(K)

D (cm-1)

E (K)

= 0exp(E/kT) = 1/(2AC) AC : Freq. of AC Field T : Temp. of max. in ” E = |D|Sz

2 = 64|D|

Ms = -8 Ms = 8

Ms = 0 Ms = 0

E = |D|Sz2

Iron(II) cubes with S = 8 ground state

SMM nonSMM nonSMM nonSMM

[Fe4(sae)4(MeOH)4] [Fe4(sap)4(MeOH)4] [Fe4(3-MeO-sap)4(MeOH)4] [Fe4(sapd)4]

N

O-

O- N

O-

O- N

O-

O-

MeO

N

O-

O-OH

Magnetization Experiments of High-spin Ferrous Cubes

g D / cm-1

[Fe4(sae)4(MeOH)4] 2.126 -0.64[Fe4(sap)4(MeOH)4] 2.261 +0.81[Fe4(3-MeO-sap)4(MeOH)4] 2.243 +1.14[Fe4(sapd)4] 2.180 +1.10

[Fe4(sae)4(MeOH)4]Fe(1)-O(1) 1.978(2) Fe(1)-O(2) 2.094(2)Fe(1)-N(1) 2.053(2) Fe(1)-O(4) 2.078(2)Fe(1)-O(9) 2.2908(18) Fe(1)-O(8) 2.2736(17)

[Fe4(sap)4(MeOH)4]·2H2OFe(1)-O(1) 2.029(2) Fe(1)-O(2) 2.045(2)Fe(1)-N(1) 2.127(2) Fe(1)-O(2)* 2.1616(15)Fe(1)-O(3) 2.2107(17) Fe(1)-O(2)* 2.2505(14)

[Fe4(3MeO-msap)4(MeOH)4]·2MeOHFe(1)-O(1) 1.991(5) Fe(1)-O(2) 2.037(4)Fe(1)-N(1) 2.104(6) Fe(1)-O(10) 2.137(4)Fe(1)-O(6) 2.238(4) Fe(1)-O(4) 2.242(5)

[Fe4(bsap)4(MeOH)4]Fe(1)-O(1) 2.036(3) Fe(1)-O(2) 2.056(3)Fe(1)-N(1) 2.123(3) Fe(1)-O(2)* 2.159(3)Fe(1)-O(2) 2.259(2) Fe(1)-O(3) 2.263(3)

Selected coordination bond distances (Å) in the cubes

N

O

O

R

Fe

Equatorially less compressed: D < 0

Equatorially compressed: D > 0Elongated octahedron

strong ligand field

week ligand field

N

O

OFe

Angular Overplap Model calculations of

Energy splitting of the 5B2g state

t2g

egb1g dx2-y2

a1g dz2

eg dxz, dyz

b2g dxy

Oh D4h

The variable p changes the equatorial ligand field strengths.

P = 0.5week LF

P = 1.0strong LF

D < 0 D > 0

saesapweek LF strong LF

Sign of DCube values

DCube < 0

easy axisZ1

Z3

Z4

Z2 sae

O-

N O-

DCube > 0

hard axisZ1

Z3

Z4

Z2 sap

O-

N O-

sap: equatorially less compressed: DFe < 0: Orthogonal alignments of four ions with easy axis

sae: Equatorially compressed: DFe > 0: Orthogonal alignments of four ions with hard axis

N

O-

O-

3,5-Cl2-sae2-

Cl

Cl

[Fe4(3,5-Cl2-sae)4(MeOH)4]

E = 26 KD = -0.29 cm-1

TB = 1.1 K

E = 30 KD = -0.33 cm-1

TB = 1.2 K

[Fe4(5-Br-sae)4(MeOH)4]

N

O-

O-

5-Br-sae2-

Br

SummaryStructurally controlled magnetic

anisotropy

•Compounds in red are SMM.• The g, C, and values were obtained from temperature dependence of the magnetic susceptibility. D values were estimated by the analyses of magnetization data at 1.8 K, supposing the only S = 8 being populated. E and TB values were estimated from the ac magnetic susceptibility measurements.

g C[emu mol-1 K]

[K]

D[cm-1]

E[K]

TB

[K]

[Fe4(sap)4(MeOH)4]·2H2O 2.261 15.43 9.56 +0.8

[Fe4(5-Br-sap)4(MeOH)4] 2.227 14.86 9.32 +0.80

[Fe4(3-MeO-sap)4(MeOH)4] 2.243 15.27 12.59 +1.15

[Fe4(sapd)4]·4MeOH·2H2O 2.180 14.29 4.57 +1.10

[Fe4(sae)4(MeOH)4] 2.126 15.55 15.98 -0.76 28 1.1

[Fe4(5-Br-sae)4(MeOH)4]·MeOH 2.209 14.57 15.68 -0.66 30 1.2

[Fe4(3,5-Cl2-sae)4(MeOH)4] 2.120 13.44 13.99 -0.67 26 1.1

[NaFeIII6]

New Cluster Molecules with higher nuclearity

N

O-

O-

MeO

5-MeO-sae2-

[FeIIFeIII6]

[FeIII2] [FeIII

3] [FeII3FeIII]

[FeIIIFeII6]

Ferric wheel of [NaFeIII6(5-MeO-sae)6(2-OMe)]ClO4

+NaClO4

[FeIII3Cl2(5-MeO-sae)3

(3-OMe)(MeOH)](3-alkoxo bridges)

[FeIIFeIII6(5-MeO-sae)6(2-OMe)6]Cl2

7FeCl2·4H2O + 6H2(5-MeO-sae) +2/7(t-Bu4N)(MnO4)

(3-alkoxo

bridge)

g(Fe3+) = 2.0 and g(Fe2+) =2.10(5)J(spoke) = -7.3 cm-1 and J(rim) = -8.7 cm-1

?

Spin frustrated system

[FeII6FeIII(5-MeO-saeH) 6(3-OMe)6]Cl3

7FeCl2·4H2O + 6(5-MeO-saeH2) +1/21(t-Bu4N)(MnO4)

2-phenoxo bridges

S = 29/2 and D = +0.53 cm-1

Angew.Chem. 2003.

Next target moleculesAir insensitive SMM

Heteronuclear SMM

The smallest SMM

Hetero-nuclear SMM

CuCl2·2H2O

[MnIII3(-O)(Br-sap)3(H2O)3]Cl

O-

N O-

Br+ MnCl2·4H2O

[MnIIICuII(Br-sap)2Cl(MeOH)]

Selected Bond Distances (Å)Mn-Cl 2.616(4) Mn-O1S 2.658(9)Other bonds 1.871(5) - 1.973(6)

Mn3+: Axially elongated octahedron for d4

Mn Cu

Magnetic susceptibility and magnetization data of

[MnIIICuII(Br-sap)2Cl(MeOH)]

Ferromagnetic interactions between Mn3+ and Cu2+ ionsS = 5/2 ground state

MO diagram of Mn3+-Cu2+ system

Tetragonally elongatedquasi D4h

Mn3

+

Square-planarquasi D4h

dxz dyz

dz2

dxy

dx2-y2dx2-y2

dz2

dxy

dxz dyz

Cu2+

O

CuMn

O

LMCTfrom O-

Cu

O N

OOMn

O O

ON

Cl

MeO

Strickt orthogonality

Quasi-single Crystal HF-EPR OF [MnIIICuII(Br-sap)2Cl(MeOH)]

-5/2-3/2-3/2-1/2 -1/21/2

1/23/2

381.5 GHz

*Magnetic field is tilted 13°with respect to the principal axis.

H. Nojiri (Okayama Univ.)

Plots of resonance fields (Hr) vs. the value of Ms

H r ge

gH0 (2M s 1)(D' 237.5B4

0 ' ) 35B40 '(4M s

3 6M s2 4M s 1)

[MnIIICuII(Br-sap)2Cl(MeOH)]

g = 2.04D = -1.70 cm-1

B40’= -0.0074 cm-1

Yamaguchi, Ishimoto (ISSP)

Single Crystal AC magnetic susceptibility [MnIIICuII(Br-sap)2Cl(MeOH)]

Packing diagrams of [MnIIICuII(Br-sap)2Cl(MeOH)]

ac projection view

bc projection view

ab projection view

Magnetization data for [MnIIICuII(Br-sap)2Cl(MeOH)] with S =5/2 ground state

Yamaguchi, Ishimoto (ISSP)

up-spin down-spin

HzHz

tunneling gap

up-spindown-spinInteger Spin Half-Integer Spin

MS = 1/ 2

MS = 3/ 2

MS = 5/ 2

MS = -1/ 2

MS = -3/ 2

MS = -5/ 2

No-spin tunneling at Hext=0X

TB = 500 mKE = 10.5 K

Summary: Nano Magnets with different sizes

Mn

Cu

Fe

[MnIIICuII] S = 5/2　with TB = 0.8 K

4核 :[FeII4] S = 8　with TB = 1.1K

6核 :[MnIII6] S = 12　with TB = 1.0 K

[FeII6FeIII] with S = 29/2　

[MnIII4MnIV

2CuII8(O)6]

1.5 nm

2.0 nm

2.5 nm

[MnIII8MnIV

4CuII8(O)16]

？

Strong correlated electron oxide clusters

S

NTunneling

-7

-6

-5

0

-4

Ms = 8

7

6

5

0

4

S

N

Nano magnets

-3 -2 -1

3 2 1

Ms = -8

Organizer  Tadashi Sugawara (University of Tokyo)

General Secretaries  Hiroki Oshio (Tsukuba University)

Kunio Awaga (Nagoya University)Kazuhito Hashimoto (Unrsity of Tokyo)